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The exterior lighting outputs are zone controlled by the front electronic module (FEM) and rear electronic module (REM) in respect to the front exterior lights being controlled by the FEM and the rear exterior lights being controlled by the REM. An additional function of the lighting system is a lamp outage function which provides the indication to the driver if certain exterior bulbs are not functioning. With a bulb inoperative, the FEM or REM will send a message to the instrument cluster and message center (if equipped) which will in turn indicate to the driver the lamp is inoperative with a lamp out indicator (with the message center a message will be displayed). To provide complete input and output functionality, each exterior lamp feature will be described individually. All exterior lighting is powered by the switched system power (SSP) feature (refer to Switched System Power[SSP]). A failure of all or any of the SSP features will cause inoperative exterior lighting. When diagnosing exterior lighting, it is essential to determine if all related symptoms and DTCs are controlled by the SSP feature.
Brake lighting is controlled by the REM. The brake pedal position (BPP) switch is hardwired to the REM. When the brake pedal is depressed, the BPP switch will input information to the REM. Then, the REM will process the information and output to the left, right, and high mounted stoplamps. Only the left and right stoplamps will provide lamp outage indication.
The vehicle's electronic functions are divided into zones. The FEM controls the front portion of the vehicle and the REM controls the rear portion of the vehicle. These systems rely heavily on the SCP communication network in order to transmit and receive signals. As a technician it is very important to understand:
- where the input (command) originates from
- All information (messages) necessary in order for a feature to operate
- which module(s) receive(s) the input or command message
- does the module which received the input (message), control the output of the feature, or does it output a message over the SCP communication network to another module
- which module controls the output of the feature
Switched System Power (SSP)
The SSP is invoked by both the FEM and REM. This function removes power from relays that provide power to the exterior lamps, interior lamps, and power door locks. This is only accomplished when both the FEM and the REM are in sleep mode. The sleep function of the FEM and REM places the modules in sleep mode when the ignition switch is in the OFF position, and no wake up (inputs) signals occur for 30 minutes. The module will not sleep if the parking lamps or the hazard lamps are active. The following relays are controlled by the SSP function: SSP1, SSP2, SSP3, and SSP4. When either the FEM or REM are not in sleep mode, all SSP relays will be energized. When energized, each relay will supply power to multiple features/functions. For additional information, go to the SSP Index for diagnosis and testing of SSP related issues. Refer to Headlamps .
Inspection and Verification
- Verify the customer concern by operating the stoplamps.
- Visually inspect for obvious signs of mechanical and electrical damage.
Visual Inspection Chart
- Blown central junction box (CJB) Fuses:
- 13 (15A)
- 7 (15A)
- 12 (20A)
- 11 (10A)
- Damaged wiring harness
- Loose or corroded connections
- Damaged BPP switch